The passenger lateral ride quality (rapid and short sideways motion) in the aft cabin of commercial jet transports is widely recognized as uncomfortable in conditions of atmospheric turbulence and gust. This is especially true of aircraft without aft-mounted engines which may significantly mitigate the effect of turbulence and gust. For long-bodied aircraft, the problem is ,even worse because the amplitudes of structural oscillations are comparatively higher for these aircraft.
It is known that these lateral gust loads react along the length of the aircraft fuselage. However, the aircraft's vertical fin (tail), due to its size, is the principal portion of the aircraft upon which the lateral gust loads react.
Numerous attempts have been made in the past to improve aircraft ride quality. These attempts sometimes featured the use of rate gyros and accelerometers to measure aft body motion (often relative to mid-body motion) and to command a corrective rudder control surface displacement. In addition, a number of conventional devices for reducing air loads have been disclosed. For example, U.S. Pat. No. 2,492,252 by Wing discloses a controller for automatically adjusting aircraft rudder trim in order to compensate for a change in power output of the aircraft's engines as a function of a measured pressure differential between the propeller slipsteam and aircraft airstream. Furthermore, U.S. Pat. No. 2,832,551 by Gille discloses a dirigible flight control system which dampens the oscillations of the dirigible's tail section relative to the front section in a manner that the rudder surface is moved to oppose the gusts which cause the tail section to oscillate.
A problem with these conventional techniques is that they do not apply corrective action until the unwanted motion already has been initiated.